After binding, roughly bound printed products such as books, paperbacks, newspapers or similar products are cut to their finished dimensions on the three unbound edges. When such products are manufactured industrially, the machines required for the entire production process are usually linked in series. In this process, printed sheets are first transferred to a gathering machine and gathered by this machine to form loose book blocks. The loose book blocks are then transferred to a binding machine in which the book blocks are bound at the spine and the bound printed products are transported by conveyor belts, on which the process of curing the adhesive used in binding takes place, to a cutting device. Further machines, such as stackers, film wrapping machines and strapping machines may be located downstream of the cutting device.
Even if the speeds of the machines and conveying means can be coordinated, irregular feeds often arise, especially on the conveyor belts between the binding machine and the cutting device, because defective printed products are extracted, specimen copies are removed and returned again by operating staff or printed products become jammed in the event of deflections, for example. This leads to an irregular supply of printed products to the cutting device in particular.
A cutting device of this type with a triple cutter is disclosed in DE3302946 C2 for example. However, such devices have the disadvantage that the number of cycles which can be achieved is significantly lower than the maximum number of cycles which can be achieved by the other machines. However, this disadvantage can be offset by feeding printed products to the cutter of the cutting device cutter in stacks. During this process, the height of the stack to be cut or the number of printed products per stack is produced by what is known as a feeder located upstream of the cutter and the stack is fed to the cutter via this feeder. The feeder comprises a hopper in which the printed products supplied by the binding machine are stacked and a pushing system which pushes stacks with a defined height or a defined number of printed products from out of the bottom of the hopper and transfers them to the cutter. To prevent overfilling of the hopper, the number of cycles of the triple cutter is set slightly higher than is required by the average performance of the binding machine. This means that the filling level in the hopper constantly reduces.
To prevent the hopper from running out of printed products, the hopper filling level is monitored. The pushing process is interrupted at a minimum admissible filling level and the cutter performs one or more empty cycles until an adequate filling level is reached once more. Alternatively, the cutting device can be stopped instead of performing empty cycles. Such devices have been tried and tested when processing thick printed products. However, in the case of thin printed products, separating the printed products exactly into stacks is an imprecise process, which can lead to errors and machine downtime.
To avoid this problem, a precisely counted stack is formed in the hopper in a further cutting device embodiment and this is subsequently pushed into the cutter. During the pushing process, the supply of additional printed products must be interrupted. An accumulating conveyor can be provided for this purpose upstream of the cutting device hopper. In this type of device the number of cycles of the cutter can also be set slightly higher than the average number of cycles required to avoid overfilling the accumulating conveyor. In this process, empty cycles can be generated from time to time or the cutter can be stopped. The counting process makes it possible to achieve precise stacks even with thin printed products. However, the associated disadvantage is the restricted performance caused by the accumulating conveyor. In other words, after accumulating, the printed products cannot be accelerated fast enough even by using a suction belt. A further disadvantage is that the accumulating conveyor may leave pressure marks on printed products with sensitive surfaces.
DE3920557 C2 proposes regulating the number of cycles of the cutting device automatically as a function of the printed products fed to the stacking hopper of the cutting device per unit of time. Despite the irregular product flow, this is intended to permit substantially trouble-free operation of the cutting device. This method admittedly minimises the number of empty cycles, but cannot avoid them completely. The method is suited to cutting devices which are loaded at relatively low speeds. If products are supplied rapidly, jams may arise when loading is resumed after interrupting the product supply, because the cutting device has only a relatively low acceleration from standstill to production speed.
Using a loading device as shown in EP0887157 should make it possible to load a cutting device which guarantees a selection of different numbers of cut products even with a non-continuous and extremely rapid succession of supplied printed products. To this end, the loading device has a counting hopper with two stacking shelves positioned one on top of the other, these being automatically controlled by the supply and removal of printed products. A pusher positioned beneath the counting hopper enables complete stacks of printed products to be fed to the cutting section in synchronisation. The control system uses signals from sensors positioned on the hopper to detect book blocks, the first sensor being positioned directly in front of the hopper, the second sensor being located on the lower stacking shelves and the third sensor being positioned on the feed table. The counting hopper can be operated in different operating modes depending on the number of copies per stack.
DE10321370 also describes a cutting device with a counting hopper, a shingled stream separator being positioned upstream of this hopper. This should make it possible to reliably process thin products which are supplied in a shingled stream.